1. Technical Field
This invention relates generally to the field of treating potable or waste water so as to reduce the pH of the water, and relates more specifically to a method and apparatus for injecting carbon dioxide into potable or waste water having a high pH level so as to reduce the pH of the water.
2. Prior Art
During its treatment phase, potable or waste water may have a high pH level, high being any pH over a pH of 9. Such a pH is unacceptable for a final, treated water product and this pH must be reduced prior to allowing the treated water into general use. For example, most water treatment plants are required to maintain an effluent pH of between 6 and 9. Therefore, any water being treated having a pH of higher than about 9 should have its pH lowered before leaving the plant.
One method for treating water so as to lower its pH is to inject carbon dioxide gas into the water. Several methods currently are used to inject the carbon dioxide into the water. The most accepted method is to inject the carbon dioxide into the water by a direct gas feed through some type of diffusion system in a recarbonation basin; in effect, a bubbler. A mechanical mixing means can be used in combination with this method for better efficiency. Another method for injecting carbon dioxide into water is to aspirate the carbon dioxide into a stream of water using a venturi type eductor. In this method, the carbon dioxide is injected into the stream of water and carried along with the stream of water to a grid system located in a basin or a pipeline.
Both the direct gas feed method and the venturi method of injecting carbon dioxide gas into water allow for the control of the pH and the stabilization of the treated water. However, it is difficult to control the efficiency of the carbon dioxide gas usage. Both of these processes require the use of a relatively large contact basin, a relatively long contact time or large amount of carrier water, all of which inherently are inefficient. Therefore, the need exists for a system for injecting carbon dioxide into water to control the pH of the water which has a greater efficiency per unit of carbon dioxide used using either less carbon dioxide or less components. A direct carbon dioxide injection method and apparatus in which the amount of carbon dioxide injected into the water stream is controlled, and the elimination of the recarbonation basin would satisfy this need, and result in increased efficiency and lower cost. It is to this need that the present invention is directed.